Figure 1.

Schematic representation of chromatin organization and H4K20 methylation. (A) Models for accessible (euchromatin) vs. condensed (heterochromatin) nucleosomal structures. (B) Two each of the histone proteins, H2A, H2B, H3, and H4, come together to form a histone octamer, which is bound by ~1.65 turns of DNA to form the nucleosome. The nucleosome bound by the H1 linker histone forms the chromatosome, which is further compacted to form chromosomes. (C) Histone protein 4 has a globular head domain and an N-terminal tail, of which the lysine (K) 20 residue can be mono, di, or tri-methylated.